Response to Ethan Siegel on Venus’ Phases
From Robert Sungenis @ www.galileowaswrong.com
First, let’s see what Mr. Siegel has to say. I will comment at the end. (NB: I’ve taken off some of
his pictures because they take up too many megs and don’t add anything to his argument).
Mr. Siegel writes:
Geocentrism: Was Galileo Wrong?
Category: Astronomy • Solar System
Posted on: September 13, 2010 8:13 PM, by Ethan Siegel
"I do not feel obliged to believe that the same God who has endowed us with sense, reason, and
intellect has intended us to forgo their use." -Galileo Galilei
While practically every scientist (and 79% of Americans) accept that the Earth and the other
planets go around the Sun, it isn't quite everyone. In fact, a number of people have recently
pointed out the following conference to me.
That's right, this November, a group of people are going to get together and try to put together as
convincing an argument as possible for geocentrism, or the model that the Sun (and all the other
planets) revolve around the Earth.
This is in stark contrast to our standard, heliocentric (Sun-centered) model, where the Earth is
just one out of many planets, all of which orbit the Sun in elliptical orbits.
Both models allow for the same very reasonable observations, all visible with the naked eye.
This includes the following:
1.
2.
3.
4.
The explanation of days and nights.
The explanation of Moon phases.
The explanation of seasons.
And finally, the observation that planets appear to "wander," or shift their position across
the night sky, relative to the fixed, background stars.
But the greatest puzzle, back in the time of Copernicus, was the problem of retrograde motion.
What's that? If you observe the planets, night-to-night, you'll find that they move across the sky
in roughly a smooth line. But if you look up at Mars during the right time of the year, you'll find
that it seems to stop in its tracks, reverse direction, go backwards for a little while, stop again,
and continue forward in roughly the original direction.
This happens for all of the outer planets, by the way, and has been confirmed hundreds of times
over the centuries.
Both models -- heliocentric and geocentric -- had a way to explain this by time Galileo came
along. The geocentric explanation came first, by way of Ptolemy.
(Image credit: Nick Strobel's Astronomy Notes.)
Rather than making a perfect circle, each planet moved about the Earth on a "circle upon a
circle." When the planet passes by closest to Earth, it appears to reverse its motion! This worked
remarkably well for predicting the positions in the sky of the planets, and was the most accurate
method we had by a lot. In fact, by even the late 1500s, 50 years after Copernicus, this geocentric
explanation was far-and-away the most superior way to predict what the positions of the planets
would be.
But the heliocentric explanation was a little more elegant, and didn't need these epicycles or
"circles-upon-circles" at all. Instead, the inner planets, in theory, moved around the Sun more
quickly than the outer ones! When an inner planet passed by an outer one, the outer one would
appear to move backwards for a brief period of time, and as the inner one continued to move
forwards, eventually the outer planet would resume its original course.
It wasn't until the early 1600s, when Kepler finally figured out that planets moved in ellipses
(and not circles) around the Sun, that finally allowed the heliocentric model to catch up with the
geocentric one in terms of predictive power.
So which was better? Was Galileo, the most passionate of all the heliocentric proponents,
justified in his adamant rejection of geocentrism?
Up until the early 1600s, I would have said "no." But right around 1609, something remarkable
happened that scientifically settled the issue.
The telescope was invented! (Note, you can repeat any or all of the following observations with
even the simplest and cheapest of telescopes.)
And one of the first things that people looked at through a telescope was the planet Jupiter. In a
single night, check out what you can see!
This video is a time-lapse of about 3 hours condensed into 10 seconds. (And it is taken with an
amateur telescope, albeit a good one.) And you'll notice that there are definitely moons orbiting
Jupiter, not Earth!
But perhaps even more striking is what you see when you look at the planet Venus. Taken over
the course of a few months, you can see the individual phases of Venus, which go all the way
from crescent to full.
Both heliocentric and geocentric models will allow Venus to run the full gamut of phases. But
you'll notice something with a telescope that you'd never notice without one: Venus appears
much larger when it's at its "new" phase and much smaller at its "full" phase.
This is different from the Moon:
and from the Sun:
which vary in size only slightly as seen from Earth.
Believe it or not, this observation is a killer for geocentrism! Why?
Because in the old geocentric model, sometimes Venus is on the same side of Earth as the Sun
(and appears new), and sometimes it's on the opposite side (and appears full).
Notice how the closeness of Venus to Earth (which determines how big Venus appears) has
nothing to do with what its phase should be! And yet, a crescent Venus is always huge, and a full
Venus is always tiny!
But, in the heliocentric model...
Venus is huge when it's a crescent because it's closer to Earth, and small when it's full because
it's on the other side of the Sun!
R. Sungenis: That Mr. Siegel hasn’t availed himself to refuting geocentrism with anymore than
these old and tired arguments about the inadequacy of the Ptolemaic model is, unfortunately,
representative of the inept caliber of people we find trying to make a case against geocentrism. If
he had searched the Internet for even a few minutes he would find that hardly anyone is using the
Ptolemaic model to support geocentrism (unless proper modifications have been made to it).
Be that as it may, let’s be fair to Ptolemy. In his day the distances to the sun, moon and planets
were not known. Hence, he could not create as accurate a model as would have been possible
had he known the distances. Had he known the distances, he simply would have made the path of
the sun around the earth the deferent of all the planets and the radius of the sun on the deferent to
the planet equal to the distance from the sun to the planet. And if he did so, his model would
have transposed into the Tychonic model, which is the model that has the planets revolving
around the sun, but the sun revolving around the earth.
The only thing Galileo’s telescope really did was destroy the crystalline spheres model of the
geocentric universe from Aristotle. Aristotle proposed that the planets stayed in their orbits by
rolling in tube-like circular structures made of crystal. These crystal-walled structures were
supposed to be impervious to penetration. But once the telescope found objects crossing their
paths (e.g., moons, asteroids, comets, etc.) the crystalline spheres model was abandoned.
All things considered, Ptolemy couldn’t have had a crystalline spheres model since his equants
and deferents were a little too wobbly for the rigidness of the spheres. In effect, Ptolemy’s model
was merely a computing device, never meant to represent the exact reality, and mainly because
neither he nor anyone else knew how far away the sun or planets were. So he did the best he
could. He rejected the Pythagorean/Aristarchus school which tried to make a heliocentric model
with perfect circles, mainly because, as Hipparchus also discovered, that heliocentric model
simply didn’t match what everyone saw in the sky. The best Ptolemy could do was put the
planets in epicycles to fit what he saw in the sky, at least for everything except Venus’ phases.
But Ptolemy was not the only one making geocentric models. The Indians and Arabs were doing
it also, and were getting very close to the truth. But since the west was so familiar with
Ptolemy’s model (and it worked to a reasonable degree), no one had really investigated the
eastern models.
But when Tycho Brahe came on the scene, we might say that the “corrected” Ptolemaic model
was finally produced. The sun’s revolution around the Earth was made the deferent of all the
planets and the problem was solved. That is because Tycho had computed the distances to the
planets much better than Ptolemy.
But Kepler stole Tycho’s forty-years worth of planet-charting (after, it is alleged, that he
murdered him by mercury poisoning) and used the charts for his favored heliocentric model
(which he was endeared to because of his occultism), and then he borrowed the idea of ellipses
from Jerome Schreiber and came reasonably close to the movements of the planets. Of course,
had Kepler applied the same elliptical orbits to Tycho’s geocentric model, Tycho’s model would
have been just as accurate.
The fact remains, we don’t use Ptolemy’s model any longer, and haven’t for about 500 years. If
anything, we use Tycho’s model or a variation of it.
Seigel: And while there are many, many, many other, subsequent observations that support the
heliocentric model and contradict the geocentric model (such as the laws of gravity,
R. Sungenis: “laws of gravity”? Again, this shows Mr. Siegel’s ignorance of science. Celestial
objects revolve around their center of mass, but even Newton wrote that the Earth could serve as
the center of mass if it was positioned correctly among all the other celestial masses.
Seigel: accelerometers on spacecraft orbiting other worlds,
R. Sungenis: I think this is a case of Mr. Seigel trying to sound scientific but not knowing what
he is talking about.
Seigel: the orbits of comets,
R. Sungenis: Only in the crystalline spheres model, as I noted above.
Seigel: the discovery of other stars and extra-solar planets, etc.), this is enough!
R. Sungenis: The only thing we have had “enough” of is Mr. Seigel’s fallacious attempts to
discredit geocentrism with his ignorance of science and history. Planets will revolve around their
stars in every place of the universe except one – the place where Earth is the center of mass for
the universe and from which everything else will then revolve around it.
Seigel: In other words, once we were able to make observations that were more sophisticated
than the simple "position of the planets over time against the background stars", the geocentric
model gives wild predictions about the apparent sizes and accelerations of the planets,
inconsistent with observations.
R. Sungenis: Correction: Copernicus’ original model was even worse than Ptolemy’s. When
Copernicus was done with his original model of heliocentrism that he started with 30 years
earlier in his Commentariolis, he ended up with 48 epicycles to Ptolemy’s 40 in his final work,
de Revolutionibus.
Seigel: But the idea that "Galileo was wrong" is now 401 years out of date, and very, very easy
to disprove. The geocentric model has yet to come up with an explanation for the apparent size
of Venus in its different phases, and the scientific conclusion is that's because it's wrong. But
perhaps someone out there knows better... any ideas?
R. Sungenis: I suggest that Mr. Seigel go back to the drawing board, as the saying goes. It would
be better if he learned a little astronomical history and physics before he decides again to enter
into this arena. The truth is, ever since geocentrism was based on a Tychonic model, Mr. Seigel’s
arguments against geocentrism are about “401 years out of date.”
For further information on Mr. Seigel, consult these websites
http://www.phys.ufl.edu/siegel/personal.html
http://www.phys.ufl.edu/siegel/personal.html
http://scienceblogs.com/startswithabang/.
http://www.phys.ufl.edu/siegel/halloween.html.